This application is based on Japanese Patent Application No. 2000-285750 filed Sep. 20, 2000, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a dynamic damper having a generally cylindrical shape, which is installed on a hollow or a solid rod member used as a vibration transmitting member such as shafts, arms and conduits in various devices and being subject to oscillation or vibration, so that vibration of the rod member is reduced or absorbed.
2. Discussion of the Related Art
There are known various kinds of rod members such as shafts or arms functioning as power transmitting members and such as conduits or pipes serving as a fluid passage. Such a rod member generally tends to oscillate or vibrate and consequently suffers from problems of resonance thereof and undesirable transmission of the excited vibration therein to the other components of a device in which the rod member is used. As a method to cope with these problems, a dynamic damper is attached to the rod member. Examples of such a dynamic damper are disclosed in JPA-2-190641, JP-B-6-37915 and JP-A-8-28627, wherein the dynamic damper has a metallic mass member having a generally cylindrical configuration and a pair of elastic support members formed on axially opposite sides of the mass member so as to extend axially outward directions, respectively. The disclosed dynamic damper is inserted onto the rod member and secured thereto at the elastic support members so that the mass member is elastically supported on the oscillating rod member via the elastic support members. Such a generally cylindrical dynamic damper is properly tuned so that the dynamic damper is capable of exhibiting effective damping characteristics with respect to a torsional or a circumferential vibration as well as a radial vibration of the rod member. Further, the mass member of the dynamic damper is less likely to drop off or released from the rod member owing to its cylindrical shape, even if the elastic support member is undesirably broken. For these advantages, the dynamic damper has been used as a dynamic damper for a drive shaft of an automotive vehicle.
In the conventional dynamic damper, the mass member is generally formed of a carbon steel by casting, or alternatively is formed by roll molding performed on a metal plate, since these materials are available at a relatively low cost and has a relatively large mass. The elastic support members are bonded to the mass member in the process of vulcanization of a rubber material for forming the elastic support member.
The conventional dynamic damper constructed as described above requires an adhesion treatment, e.g., an application of the adhesive on the circumferential surface of the mass member, upon bonding the elastic support member to respective portions of the mass member in the above-indicated vulcanization of the material. This may cause deterioration in terms of efficiency and cost of manufacture of the dynamic damper.
In the light of these drawbacks of the conventional dynamic damper, it is considered to modify the conventional dynamic damper to comprise an elastic covering layer which is integrally formed with the elastic support members so as to cover substantially entire area of the outer surface of the mass member, so that the mass member is fixed to the elastic support member without using the adhesion applied between the elastic support member and the mass member. However, the omission of the adhesive treatment leads to difficulty in attaining practically sufficient fixing or bonding strength between the elastic support members and the mass member. Described in detail, the elastic support members and the mass member which are not bonded with each other via the adhesive layer, are likely to be displaced relative to each other at the interface therebetween upon application of a relatively large vibrational load to the dynamic damper. This may possibly cause deterioration of vibration damping effect of the dynamic damper.
It is therefore an object of the present invention to provide a dynamic damper which is novel in construction and which permits a high fixing or bonding strength between a metallic mass member and an elastic support member with no adhesive treatment performed on the metallic mass member.
The above object may be attained according to the following modes of the invention, each of which is numbered like the appended claims and depends from the other mode or modes, where appropriate, to indicate possible combinations of elements or technical features of the invention. It is to be understood that the present invention is not limited to those modes of the invention and combinations of the technical features, but may otherwise be recognized based on the teachings of the present invention disclosed in the entire specification and drawings or that may be recognized by those skilled in the art in the light of the present disclosure in its entirety.
(1) A dynamic damper mounted on a rod-shaped oscillating member, including: (a) a generally cylindrical metallic mass member formed of sintered metal or forging, and disposed radially outwardly of the oscillating member; (b) a pair of elastic support members formed on and extending axially outwardly from axially opposite sides of the metallic mass member to elastically support the metallic mass member with respect to the rod-shaped oscillating member; and (c) an elastic covering layer integrally formed with the pair of elastic support members and being fixed in close contact with a substantially entire area of a surface of the metallic mass member without using an adhesive, for covering the substantially entire area of the surface of the metallic mass member, the metallic mass member having at least two slits extending through a wall thickness thereof, the at least two slits being open in and extending axially inwardly from axially opposite end faces of the metallic mass member, respectively, and being filled with the elastic covering layer, the metallic mass member further having inclined planes formed at radially inner edges of circumferentially opposite open-end edge portions of each of the at least two slits, each of the inclined planes extending over an inner surface of the corresponding slit, the corresponding axial end face of the metallic mass member and the inner circumferential surface of the metallic mass member, to chamfer the radially inner edge of the corresponding open-end edge portion.
In the dynamic damper constructed according to the above mode (1) of the present invention, the metallic mass member is formed of sintered metal or forging. This arrangement permits a relatively high level of surface roughness of the metallic mass member of the dynamic damper of the present invention in comparison with a metallic mass member formed by casting or pressing. Accordingly, the elastic covering layer fixed in close contact with the rugged surface of the metallic mass member is firmly secured to the metallic mass member owing to a mechanical fixing force caused by engagement of the rugged surface of the metallic mass member with the inner surface of the elastic covering layer which is rugged corresponding to the rugged surface of the metallic mass member upon vulcanization of a rubber material to form the elastic covering layer, resulting in elimination of the adhesive treatment. Various kinds of known sintered metallic materials, including pure iron type, iron-carbon type, and iron-copper type, may be employed for the metallic mass member of the dynamic damper of the present invention, taking into account the required mass of the metallic mass member, the manufacturing cost, working conditions of the dynamic damper and the like. Further, various kinds of known forging or forged members, such as a carbon steel may be used as the metallic mass member, and the metallic mass member may be formed by hot forging or alternatively by cold forging. The employed forging should be subjected to a scale removal treatment by a shot blasting method or the like. In addition, the metallic mass member may be provided with tapered inner and outer circumferential surfaces, as needed, thereby facilitating release of the metallic mass member from the mold.
In the dynamic damper constructed according to the present invention, the metallic mass member has at least two slits formed at axially opposite side portions thereof, respectively. That is, each of the axially opposite side portions of the metallic mass member has at least one slit formed therethrough and open in the corresponding one of the axially opposite end face of the mass member. These slits formed through the metallic mass member are filled with the elastic covering layer. The parts of the elastic covering layer which fill the slits, function to directly connect the radially inner part of the elastic covering layer formed on the inner circumferential surface of the metallic mass member and the radially outer part of the elastic covering layer formed on the outer circumferential surface of the metallic mass member. This arrangement permits further improved fixing stability of the elastic covering layer to the metallic mass member, without requiring the use of the adhesive interposed between the elastic covering layer and the metallic mass member.
Namely, the dynamic damper constructed according to the present invention permits a sufficiently enhanced fixing stability between the elastic covering layer and the metallic mass member, while assuring elimination of the adhesive treatment and a resultant reduced manufacturing cost, owing to the surface characteristics of the metallic mass member formed of sintered metal prepared by heating the compressed metallic power, or formed of forging subjected to the scale removable treatment. It should be appreciated that the process for removing the scale of the forging is generally performed upon manufacturing the forging. Therefore, the present invention requires no specific facilities or manufacturing process for performing the scale removal treatment on the metallic mass member, and accordingly no increase in the manufacturing cost.
In the presence of the inclined planes formed at the radially inner edges of the circumferentially opposite open-end edge portions of the slits of the metallic mass member, the dynamic damper according to this mode of the invention is less likely to suffer from or free from a possible problem of the deterioration in stability of the elastic support members due to the presence of the slits in the metallic mass member. Described in detail, a dynamic damper including a cylindrical metallic mass member and the two elastic support members which are formed axially opposite sides of the metallic mass member for elastically supporting the metallic mass member, is likely to suffer from a stress concentration generated at or near a boundary between elastic support members and the axially opposite end faces of the metallic mass member. If the slits are formed in the metallic mass member so as to open in the respective axially opposite end faces of the metallic mass member, the edge portions are formed at circumferentially opposite sides of the open end portion of each slit. That is, the circumferentially opposite open-end edge portions of each slit are provided in the axially opposite end faces of the metallic mass member. These edge portions of the metallic mass member may possibly cause further stress concentration generated at or near a boundary between the elastic support members and the edge portions of the metallic mass member, resulting in insufficient durability of the elastic support member. To cope with this problem, the dynamic damper according to this mode of the invention is arranged such that the radially inner edge of each of the open-end edge portions of the metallic mass member is chamfered to provide the inclined plane. The arrangement is effective to ease the stress concentration generated at or near the boundary between the elastic support member and the edge portions and to prevent occurrence of defects such as cracking in the elastic support members. Thus, the dynamic damper according to this mode of the invention can exhibit a desired durability of the elastic support members.
In this respect, inclined planes are formed only at the radial inner edges of the open-end edge portions of the metallic mass member and are arranged to extend not to reach the outer circumferential surface of the metallic mass member. This arrangement is effective not only to prevent a change of the spring characteristics of the elastic support member due to the formation of the inclined planes, but also to restrain decrease of the mass of the metallic mass member, resulting in elimination of adverse effect of the formation of the inclined planes on the vibration damping characteristics of the dynamic damper.
Various kinds of rubber materials may be employed for forming the elastic support member and the elastic covering layer which are integrally formed with each other, depending upon required vibration damping characteristics of the dynamic damper of the present mode of the invention. For instance, a rubber material such as NR (natural rubber), SBR (styrene-butadiene rubber) or BR (butadiene rubber), or a mixture of any two or more thereof may be suitably used. The elastic covering layer is only required to cover substantially the entire area of the surface of the cylindrical metallic mass member, and does not necessarily require to cover local portions of the metallic mass member to which supporting members of the mold are butted, for supporting and positioning the metallic mass member in the mold. The thickness of the elastic covering layer is determined to be held preferably within a range of 0.5-5 mm, more preferably within a range of 1-3 mm, in view of the fact that the elastic covering layer having an excessively small thickness may deteriorate its durability or its fixing strength to the cylindrical metallic mass member, while an excessively large thickness of the elastic covering layer may lead to an undesirable increase in the size of the dynamic damper.
In order to form and closely secure the elastic covering layer on and to the outer circumferential surface of the metallic mass member, it is desirable to integrally form the elastic covering layer and the elastic support members by vulcanizing a rubber material to form the elastic covering layer and the elastic support member in a mold wherein the metallic mass member is placed in position. In this respect, the metallic mass member does not need to be subjected to the adhesive treatment, but may be subjected to washing or degreasing treatments, as needed.
(2) A dynamic damper according to claim 1, wherein each of the slits has an axial length of one-fourth to three-fourths of an axial length of the metallic mass member.
If each slit has its axial length smaller than one-fourth of the axial length of the cylindrical metallic mass member, the corresponding part of the elastic covering layer which fills the slit may possibly function insufficiently to connect the radially inner and outer parts of the elastic covering layer with each other. If the slit has its axial length larger than three-fourths of the axial length of the cylindrical metallic mass member, on the other hand, it makes it difficult to obtain sufficient mass of the metallic mass member. In this mode (2), the axial length of each slit is limited within the range of one-fourth to three-fourths of the axial length of the metallic mass member, thereby assuring a sufficient mass of the metallic mass member, while ensuring sufficient fixing strength between the metallic mass member and the elastic covering layer. In order to attain the sufficient mass of the metallic mass member and the sufficient fixing strength between the metallic mass member and the elastic covering layer, in a relatively higher level, the axial length of each slit is preferably limited within a range of one-third to two-thirds, more preferably limited within a range of one-third to a half of the axial length of the metallic mass member.
The circumferential positions of the slits in the metallic mass member are not particularly limited. For instance, the circumferential positions of the slits formed on one side of the metallic mass member may coincide with, or alternatively differ from those of the slits formed on the other side of the metallic mass member. In the former case, the axial length of the slits needs to be smaller than about a half of the axial length of the metallic mass member. In the latter case, the slits can have the axial length of not smaller than about a half of the axial length of the metallic mass member, within the above-indicated upper limit.
(3) A dynamic damper according to the above-indicated mode (1) or (2), wherein each of the inclined planes has a size which is determined such that the corresponding radially inner edge is chamfered by 1.0 mm or more at respective three lines of intersections of adjacent ones of the inner surface of the corresponding slit, the corresponding axial end face of the metallic mass member and the inner circumferential surface of the metallic mass member.
If the inclined plane is excessively small in size, the inclined plane is less likely to function to reduce or ease the level of the stress concentration in the boundary between the elastic support member and the circumferentially opposite open-end edge portions of each of the slit of the metallic mass member. On the other hand, if the inclined plane is excessively large in size, it becomes difficult to obtain a required mass of the metallic mass member sufficiently. In this mode (3), the radially inner edge of each of the open-end edge portions is chamfered by 1.0 mm or more at respective three lines of intersections of the adjacent ones of the above-indicated three surfaces, namely including a first line of intersection of the inner surface of the slit and the axial end face of the metallic mass member, a second line of intersection of the inner surface of the slit and the inner circumferential surface of the metallic mass member, and a third line of intersection of the axial end face of the metallic mass member and the inner circumferential surface of the metallic mass member. This makes it possible to exhibit improved durability of the elastic support member, owing to the stress-concentration-easing effect of the resultant inclined plane, while assuring a sufficiently large mass of the metallic mass member. Preferably, each of the inclined planes has a size which is determined such that the corresponding radial inner edge is chamfered by 2.0 mm or more at respective three lines of intersections of adjacent ones of the inner surface of the corresponding slit, the corresponding axial end face of the metallic mass member and the inner circumferential surface of the metallic mass member. In this respect, the upper limit of the size of the inclined plane is determined such that the inclined plane extends at the lines of intersection of the inner surface of the slit and the axial end face of the metallic mass member with a length which is smaller than the dimension of the wall thickness of the metallic mass member.
(4) A dynamic damper according to any one of the above-indicated modes (1)-(3), wherein the surface of the metallic mass member has a ten-point mean roughness Rz within a range from 30 xcexcm to 200 xcexcm.
Namely, an excessively small Rz value of the surface roughness of the metallic mass member leads to difficulty in obtaining a sufficient fixing stability between the metallic mass member and the elastic covering layer, while an excessively larger Rz value of the surface roughness of the metallic mass member may lead to deterioration of efficiency and increased cost of manufacture. In the above mode (4), the metallic mass member is arranged to have a ten-point mean roughness Rz within a range from 30 xcexcm to 200 xcexcm, thereby effectively providing a metallic mass member which assures sufficient bonding stability between the metallic mass member and the elastic support members. Preferably, the metallic mass member is arranged to have a ten-point mean roughness Rz within a range from 50 xcexcm to 100 xcexcm, resulting in further improved efficiency in obtaining the desired bonding stability between the metallic mass member and the elastic covering layer.
(5) A dynamic damper according to any one of the above-indicated modes (1)-(4), wherein the pair of elastic support members have a tapered cylindrical shape such that the elastic support members extending axially outwards and radially inwards from the axially end faces of the metallic mass member.
In the dynamic damper according to the above mode (5), the use of the tapered elastic support members facilitates tuning of the spring characteristics of the dynamic damper in various directions including an axial direction, a radial direction, a bending direction and a torsional direction, by adjusting a taper angle or a wall thickness of the elastic support members. Further, the taper angle or the axial length of the elastic support members may be suitably adjusted depending upon the outside diameter of the rod member on which the dynamic damper is installed. This makes it possible to use the same metallic mass member for different oscillating rod members which have different outside diameters.